1. Field of the Invention
The present invention relates to a valve gear of an internal combustion engine.
2. Description of the Related Art
An intake valve and an exhaust valve of an internal combustion engine are driven so as to be opened and closed by a power taken out from a crank shaft of the internal combustion engine. In recent years, it is tried to drive the intake valve and the exhaust valve by an electric motor to open and close the valves. For example, there has been proposed a valve gear which opens and closes the intake valve by rotating a cam shaft by a stepping motor (Japanese Patent Application Laid-Open (JP-A) No. 8-177536). In addition, JP-A No. 59-68509 exists as a prior art document relevant to the present invention.
When the intake valve and the exhaust valve are opened and closed by driving the cam mechanism by the electric motor, it is necessary to output a driving force against a torque applied to the cam mechanism based on a repulsive force of a valve spring provided for each of the valves (hereinafter, this torque is referred to as a valve spring torque), from the electric motor. Accordingly, when the valve spring torque is increased, an increase of an electric power consumption and an increase of an electric motor rating are generated.